Laser projection system and method

ABSTRACT

A laser projection system for projecting an image on a workpiece includes a photogrammetry assembly and a laser projector, each communicating with a computer. The photogrammetry assembly includes a first camera for scanning the workpiece, and the laser projector projects a laser image to arbitrary locations. Light is conveyed from the direction of the workpiece to the photogrammetry assembly. The photogrammetry assembly signals the coordinates light conveyed toward the photogrammetry assembly to the computer with the computer being programmable for determining a geometric location of the laser image. The computer establishes a geometric correlation between the photogrammetry assembly, the laser projector, and the workpiece for realigning the laser image to a corrected geometric location relative to the workpiece.

PRIOR APPLICATION

This application claims priority to U.S. patent application Ser. No.14/954,117 filed on Nov. 30, 2015, which is a continuation of U.S.patent application Ser. No. 13/652,735 filed on Oct. 16, 2012, now U.S.Pat. No. 9,200,899 issued on Dec. 1, 2015 and U.S. Provisional PatentApplication No. 61/614,252 filed on Mar. 22, 2012.

FIELD OF USE

This application relates generally to a laser projection system for usein an industrial environment. More specifically, this applicationrelates to projecting a laser template on a workpiece with theassistance of a photogrammetry assembly.

BACKGROUND

Photogrammetry processes and assemblies have been used to identifylocations of objects in various settings. In some instances,photogrammetry has been found useful in the manufacture ofsemiconductors for use in computer-based objects. However,photogrammetry has not proven useful in the manufacture of large scaleobjects in a mass production setting.

Alternatively, laser projectors have been used to project assemblytemplates on objects as an assembly aid in the manufacture of massproduction products. However, projecting templates has also not beenuseful on a mass production scale where various workpieces are beingproduced and limited opportunity exists to project a geometricallyaccurate projection image. Therefore, manufactures of original equipmentcontinue to use physical, and in some instances, steel templates todirect work performed on workpieces.

Therefore, a need exists to enhance both the ability to locate an objectin a precise geometrical relationship to a laser projector to accuratelyproject a template for use as an assembly aid.

SUMMARY

A laser projection system and method for projecting an image on aworkpiece includes the use of a photogrammetry assembly and a laserprojector each communicating with a computer. The photogrammetryassembly includes a first camera for scanning the workpiece. The laserprojector projects a laser image to arbitrary locations with the laserimage being readable by the camera. The photogrammetry assembly signalsthe coordinates of the work piece to the computer by scanning lightconveyed from the direction of the workpiece. The computer isprogrammable for determining a geometric location of the workpiece fromthe light conveyed from the direction of the workpiece. The computerestablishes geometric correlation between the photogrammetry assembly,the laser projector, and the workpiece and signals the laser projectorto project a template onto a geometric desirable location of theworkpiece.

For the first time, a low cost method of generating a laser templateonto the workpiece has been achieved. The use of a photogrammetry systemto assist locating a laser projected template within a geometriccoordinate system in an industrial setting reduces cost while increasingthe quality and dimensional accuracy of work performed on a workpiece.Where affixing a physical template to the workpiece only providesgeneral dimensional accuracy, the subject method of projecting a laserimage or template with the assistance of a photogrammetry deviceprovides a manufacturing tolerance of less than one millimeter.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings:

FIG. 1 shows a first embodiment of the laser projection system of thepresent invention;

FIGS. 2a and 2b show an alternative embodiment of the laser projectionsystem of the present invention;

FIG. 3 shows a reflective probe for use with the second embodiment;

FIG. 4 shows a lens view of a camera associated with a photogrammetryassembly associated with the laser projection system; and

FIGS. 5a and 5b show an alternative embodiment of the laser projectionsystem of the present invention.

DETAILED DESCRIPTION

A laser projection system for projecting an image on a workpiece isgenerally shown at 10 of FIG. 1. The laser projection system includes aphotogrammetry assembly 12 and a laser projector 14, each of whichcommunicates via a computer 16. The computer 16 communicates with thelaser projector 14 by way of electrical circuit 18 and with thephotogrammetry assembly 12 by way of electrical circuit 20. Although theelectrical circuits 18, 20 are represented as hard wires in thisembodiment, it should be understood by those of skill in the art thatradio frequency or equivalent transmission between the computer 16, thephotogrammetry assembly 12 and the laser projector 14 is within thescope of this invention.

The photogrammetry assembly includes a first camera, 22 and, in thisembodiment, a second camera 24. It is contemplated by the inventor thatalternative embodiments may make use of only a first camera 22 as willbe explained further below. One type of camera contemplated by theinventors is an industrial camera model acA2500-14GM manufactured byBasler AG. However, other industrial type cameras having equivalentfunctionality is suitable for use with the inventive projection system10.

The photogrammetry assembly 12 is adapted to scan and take an image of aworkpiece 26 and a surrounding environment 28 for the purpose oflocating the workpiece 26 in a three-dimensional coordinate system.

The laser projector 14 projects a laser image to arbitrary locations 30with at least some of the laser image being projected onto the workpiece26. The laser image takes the form of a plurality of laser beams, laserpatterns, or manufacturing template, or combinations thereof.

The laser image generated by the laser projector 14 is readable by thephotogrammetry assembly 12. More specifically, the laser image isreadable by the first and second camera 22, 24. The first and secondcameras 22, 24 are separated a known distance by a spacer bar 32manufactured from the material not subject to dimensional variations dueto temperature fluctuations. In one embodiment, the spacer bar 32 ismanufactured from a uni-directional carbon fiber to provide temperatureresistance to dimensional variation.

The first and second cameras 22, 24 identify the arbitrary locations 30onto which the laser image is projected by the laser projector 14 bytriangulating the image and signaling the computer 16 to calculate wherethe arbitrary locations 30 are located in a three-dimensional coordinatesystem.

The computer 16 is programmed to calculate the geometric correlationbetween the photogrammetry assembly 12, the laser projector 14 and theworkpiece 26 by way of a signal transmitted from the cameras 22, 24 ofthe scanned arbitrary locations 30 onto which the laser image isprojected. Additional accuracy is achievable by manipulating the laserprojector 14 to project a laser image onto the various features such as,for example, corners or apertures defined by the workpiece 26 andscanning the laser image as set forth above. Once the computer 16establishes a geometric correlation between the photogrammetry assembly12 the laser projector 14 and the workpiece 26, the laser image iscorrected to a geometric location relative to the workpiece 26 and isused as a template for an assembly aid to perform work on the workpiece26. For example, the laser template identifies the location of a weldoperation, a machine operation, or other work intended to be performedon the workpiece 26.

Once the laser template has been projected onto a desired location uponthe workpiece 26, the computer 16 periodically prompts the projector 14to project a laser image to arbitrary locations 30 from which thephotogrammetry assembly 12 scans and signals the computer 16 tocalculate the geometric correlation between the photogrammetry assembly12, the laser projector 14, and the workpiece 26 to verify none of theseitems have been moved, there has been no drift of the image, and thatthe laser template is projected in the correct geometric location on theworkpiece 26. In this manner, the accuracy of the laser projection ofthe template is repeatedly updated during the manufacturing operation.

An alternate embodiment of the present invention, wherein like elementsinclude like element numbers, is generally shown at 110 of FIGS. 2a and2b . In this embodiment, the photogrammetry assembly 12 includes a lightsource 34 (FIG. 4) transmitting light that is readable by thephotogrammetry assembly 12 separate from the laser image. However, it iscontemplated by the inventor that the light source 34 transmits light ina similar wave-length range as that of the laser projector 14. Morespecifically, it is contemplated that green light having a wave lengthrange between 540 and 520 nanometers is transmitted by both the lightsource 34 and the laser projector 14. It is further contemplated by theinventor that the light source 34 includes a plurality of light emittingdiode spaced around each camera lens 36 of the first and second cameras22, 24 as best represented in FIG. 4. However, it should be understoodby those of ordinary skill in the art that the light source 34 can beseparate from the photogrammetry assembly 12 as will be explainedfurther below.

Referring again to FIGS. 2a and 2b , the light source 34 transmit lighttoward the workpiece 26 onto which reflective targets 38 are temporarilyaffixed. The reflective targets 38 are contemplated to beretroreflective targets for reflecting light back toward thephotogrammetry assembly 12 into the camera lens 36 of the first andsecond cameras 22, 24 so that the photogrammetry assembly 12 signal thecomputer 16 the location of the reflective targets 38 allowing thecomputer 16 to calculate the precise location of the workpiece 26 in ageometric coordinate system. In this embodiment, the inventorcontemplates the reflective targets 38 be encoded to enable a computerto identify which reflective targets 38 are signaling the photogrammetryassembly 12. For example, one method of encoding the reflective targets38 is by way of two reflective elements disposed upon individualreflective targets 38 and spaced a known distance enabling the computer6 to read two reflective images spaced a known distance from anindividual reflective target 38. It is also believed that encoding thereflective targets 38 reduces the probability of the photogrammetryassembly 12 reading reflections from the environment 28 in errorrendering an incorrect calculation of the location of the workpiece 26in the coordinate system.

The light source 34 periodically emits light contemplated to be in theform of a flash so that the computer 16 can continuously calculate thelocation of the workpiece 26 within the geometric coordinate system.Once the workpiece 26 is established within a geometric coordinatesystem, the laser projector 14 projects a laser image to arbitrarylocations as set forth in the previous embodiment. Therefore, thephotogrammetry assembly 12 scans both light reflected from thereflective targets 38 and the laser image projected on arbitrarylocations 30 by the laser projector 14 to accurately determine spatialrelationship within a geometric coordinate system of the photogrammetryassembly 12, the laser projector 14, and the workpiece 26. It should beunderstood by those of skill in the art that the light source 34 canalso transmit light from the location of the reflective targets 38 areaffixed. In this manner, light emitting diodes 34 would replace thereflective targets 38 and transmit light directly to the photogrammetryassembly 12. It should be understood that when the term reflect orreflector is used transmitting light as described above is also includedso that light is conveyed from the direction of the workpiece.

Included in this embodiment is a probe 40 best represented in FIG. 3.The probe 40 includes a contact element 42 disposed upon a distal end 44of a shaft 46. The reflective target 48 is disposed on an opposite endof the shaft 46 from a contact element 42. The reflective target 48 iscontemplated to include a plurality of arms 50 each having encodedreflectors 52. The use of four reflectors 52 has proven to improve theaccuracy of the measurements of the geometrically relevant features onthe workpiece, particularly when the reflectors 52 are spaced from anaxis of the probe defined by the contact element 42. The reflectors 52are encoded by locating a plurality of reflectors 52 on each arm 50spaced by a known distance. However, alternative methods of encoding mayalso be used such as, for example, altering the reflectivity of anindividual reflector 52. By encoding the reflectors 52, thephotogrammetry assembly 12 is able to determine which specific probe 48is reflecting light from the light source 34 to the photogrammetryassembly 12. Encoding is desirable when a plurality of probes 40 areused to identify various features on the workpiece 26 as will beexplained further below.

Referring again to FIGS. 2a and 2b , the probe 40 is shown reflectinglight received from the light source 34 to the first and second camera22, 24, allowing the computer 16 to determine the location of the probe40 in the geometric coordinate system in which the workpiece 26 exists.The contact element 42 of the probe 40 is manually touched to aparticular feature on the workpiece 26. This approach streamlines thedetermination of the important features or datums on the workpiecenecessary for performing work on the workpiece in a dimensionallyaccurate manner, and reduces the time required to project the lasertemplate onto the workpiece. For example, the contact element 42 istouched to an edge of an aperture (not shown) that is a datum from whicha work location must be accurately correlated. Once the computer 16calculates the location of the probe 40, the laser projector 14transmits a laser image in the form of a template further increasing theaccuracy of the location of the laser image on the workpiece 26. Thecontact element 42 is touched to various edges or contours of a specificelement to further define the location of the element by way of theprobe 40 again enhancing the accuracy of the template projected on theworkpiece 26 by the laser projector 14. Alternatively, the contactelement 42 includes different shapes and sizes mirroring the variousfeatures of the workpiece 26 requiring location identification insidethe coordinate system.

A still further embodiment of the projection system is generally shownat 210 of FIGS. 5a and 5b . In this embodiment, the photogrammetryassembly 12 makes use of a single camera 22 and communicates with thelaser projector 14 and the computer 16 as explained above. Because asingle camera 22 is used to scan the workpiece 26, it is desirable toestablish a geometric scale of the relative position of the workpiece26. As such, a scale bar 54 having scale reflective targets 56 spaced aknown distance on a scale bar 54. Through triangulation with the spacedscale reflective targets 56 and the camera 22, the computer 16 is ableto establish a geometric scale of the workpiece 26 in a geometriccoordinate system. As set forth above, the workpiece surface isidentified by temporarily affixing reflective targets 38 which areencoded. The light source 34 transmits light to the reflective targets38 and to the scale reflective targets 56 and the photogrammetryassembly scans the reflective image to signal the computer 16 thecoordinates of the workpiece 26, allowing the computer 16 to correlatethe photogrammetry assembly 12, the laser projector 14, and theworkpiece 26 in a geometric coordinate system. This allows the laserprojector 14 to project a laser template upon the workpiece 26 as setforth above. It should be understood to those of skill in the art thatthe probe 40 may also be used in combination with the scale bar 54 andscale reflective targets 56 to accurately determine precise location ofvarious features of the workpiece 26.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation. It isnow apparent to those skilled in the art that many modifications andvariations of the present invention are possible in light of the aboveteachings. It is, therefore, to be understood that the invention may bepracticed otherwise than as specifically described.

1. A laser projection system comprising: a laser projector configured toproject a laser image onto a workpiece; an optical sensor assemblyconfigured to periodically emit light toward the workpiece and opticallydetect the location of a plurality of reference targets thereon; and acomputer electrically coupled to the laser projector and the opticalsensor assembly, the computer being configured to perform the followingmethod steps: calculate the location of the workpiece within a geometriccoordinate system based on the location of the plurality of referencetargets as detected by the optical sensor assembly, cause the laserprojector to project a template onto a desired geometric location of theworkpiece for a manufacturing operation, monitor for relative movementbetween the workpiece, the laser projector, and the optical sensorassembly, correct the template being projected onto the workpiece. 2.The laser projection system of claim 1 wherein the geometric coordinatesystem is a three-dimensional coordinate system.
 3. The laser projectionsystem of claim 1 wherein the optical sensor assembly comprises aphotogrammetry assembly including first and second cameras that arespaced apart from each other by a fixed distance.
 4. The laserprojection system of claim 1 wherein the emitted light includes awavelength of between 520 nm and 540 nm.
 5. The laser projection systemof claim 1 wherein the computer is further adapted to determine ageometric correlation between the optical sensor assembly and the laserprojector.
 6. The laser projection system of claim 1 wherein theplurality of targets includes encoded retroreflective targets.
 7. Thelaser projection system of claim 1 wherein the template is amanufacturing template for performing a weld operation or a machineoperation on the workpiece.
 8. A method for projecting an image onto aworkpiece comprising: providing a laser projector configured to projecta laser image onto the workpiece; periodically emitting light toward theworkpiece for detection by an optical sensor assembly; using the opticalsensor assembly for optically detecting the location of a plurality ofreference targets supported on the workpiece; calculating the locationof the workpiece within a geometric coordinate system based on thelocation of the plurality of reference targets; causing the laserprojector to project a template onto a desired geometric location of theworkpiece for a manufacturing operation; monitoring for relativemovement between the workpiece, the laser projector, and the opticalsensor assembly; and correcting the template being projected onto theworkpiece based upon movement of the .
 9. The method set forth in claim8 further including determining a geometric correlation between theoptical sensor assembly and the laser projector.
 10. The method setforth in claim 8 wherein the geometric coordinate system is athree-dimensional coordinate system.
 11. The method set forth in claim 8wherein the optical sensor assembly includes a photogrammetry assemblycomprising first and second cameras that are spaced apart from eachother by a fixed distance.
 12. The method set forth in claim 8 whereinthe emitted light includes a wavelength of between 520 nm and 540 nm.13. The method set forth in claim 8 wherein the plurality of targetsincludes encoded retroreflective targets.
 14. The method set forth inclaim 8 wherein emitting light toward the workpiece includes scanning aspace comprising the workpiece for establishing a background image andwherein optically detecting the location of the plurality of encodedretroreflective targets includes subtracting the background image fromlight reflected by the plurality of encoded retroreflective targets. 15.The method set forth in claim 8 wherein the template is a manufacturingtemplate for performing a weld operation or a machine operation on theworkpiece.